<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        html,body,svg { height:100%; margin: 0; padding: 0; display:block; }

    </style>
</head>
<body>
    <svg viewBox="0 0 200 100" xmlns="http://www.w3.org/2000/svg">
        <path fill="none" stroke="lightgrey"
          d="M20,50 C20,-50 180,150 180,50 C180-50 20,150 20,50 z" />
      
        <rect width="5" height="5" fill="red" >
          <animateMotion dur="10s" repeatCount="indefinite"
            path="M20,50 C20,-50 180,150 180,50 C180-50 20,150 20,50 z"
            keyPoints="0;0.2;1" keyTimes="0;0.5;1" />
        </rect>
      </svg>
      
</body>
</html>